An actuator is a mechanical component that performs some real-world activity. For that, it uses some kind of energy and a mechanism as the core system. Actuators are, by meaning components that are used to actuate something or to put something in motion.
A very simple example of an actuator is a motor that takes electricity as the source of energy and starts rotating a shaft on its axis. When embedded with some semiconductor components, actuators can perform spectacular actions.
Following are five major types of actuators:
Electric actuators: Electric actuators convert electricity in to motion. Motor is the best example of this kind of actuator where it takes electricity as the source of energy.
Hydraulic actuators: Hydraulic actuators convert hydraulic power into motion. Usually, fluid cylinders are used to produce hydraulic power that is capable enough to lift up a significant weight. Crains and bulldozers are the most common use cases of hydraulic actuators.
Pneumatic actuators: Pneumatic actuators use pressure as the source of power to produce motion. These actuators are usually powered by vacuum or compressed air and the output is used to produce linear, angular or rotary motion.
Mechanical actuators: Mechanical actuators use some kin of motion to produce some other kind of motion. Gears, rails, conveyer belts, pullies etc are some popular examples of mechanical actuators.
Thermal actuators: Thermal actuators use thermal energy to produce motion. A minor or major change in temperature can cause physiological changes in an object. This behaviour is utilized by thermal actuators to produce motion.